(1) Field of the Invention
This invention relates to improving the physical properties of cotton cellulose containing textiles. More specifically this invention relates to products and the process of imparting improved balances of textile properties wherein improved levels of abrasion resistance, breaking strength and tearing strength are combined with high levels of resilience. This superior balance of textile properties is achieved by modification of a conventional chemical treatment of cellulosic textiles.
(2) Description of the Prior Art
It is well known to impart durable wrinkle resistance to cellulosic fabric such as cotton fabric by impregnation with an aqueous solution of a suitable thermo-setting resin precondensate or a cellulose crosslinking agent, usually accompanied by an appropriate catalyst, and eventually curing the impregnated fabric. Such treatment has been effective in improving the wrinkle resistance and the shape holding properties of cotton fabrics and has resulted in greatly increased demand for "Easy-Care", "Wash-And-Wear", "Permanent-Press", and "Durable-Press" cotton fabrics, that are desired in today's textile market.
A variety of processes has been developed and used for improving wrinkle resistance or wrinkle recovery of fabrics and garments. These processes are known in general as pad-dry-cure chemical resin treatments, wherein one or more reagents are applied to the fabric through padding, and the fabrics are partially dried before the resin is cured.
The conventional thermo-setting chemical or resin systems (either post-cured or precured) result in embrittlement and reduction of mobility of the microstructural units of cellulosic fibers to such an extent that tearing strength, breaking strength and abrasion resistance are seriously impaired. Tearing strength is often reduced by 50%, breaking strength by 50-60%, and abrasion resistance by 75-85%.
Over the last several years, considerable research has been conducted to find ways of overcoming this problem without compromising the wash-wear or durable-press performance of the fabric. Many variations of pad-dry-cure processing have been developed in attempts to solve the problem. These include processes involving a multistage padding and curing, processes involving a pad and wet-fixation prior to cure, and processes involving polymeric additives. The results achieved through all of these processes have been marginal, and the processes have often been found to be crumblesome and expensive.
A particularly promising approach to the production of easy-care, durable-press fabric has involved a wet fixation of resin-forming, crease-proofing agents such as formaldehydemelamine precondensate, as disclosed in Textile Research Journal 37, 70 (1967) and in U.S. Pat. No. 3,138,802. In this type of process the fiber system such as cotton fabric is protected against an excess strength loss by fixation of a suitable resin forming and crease proofing agent within the fibers while they are wet and swollen. In the laboratory process the fabric, padded with a solution of reagents at pH=2 is heated in a moist atmosphere to achieve fixation of the N-methylol reagents. Part of the resin in contact with the cotton is firmly fixed in the cotton fibers and the fabric at this stage; after rinsing and introduction of a catalyst and softener, the fabric can be cured immediately or stored prior to cure at elevated temperature. Wet fixation processes have generally been cumbersome, or have required special processing equipment.
The use of nonreactive or co-reactive additives for the purposes of obtaining improved abrasion resistance on durable-press fabrics is discussed in Textile Research Journal 37, 253 (1967). This type of approach is exemplified in U.S. Pat. No. 3,877,872 which calls for the inclusion of triethylene glycol dimethyl ether in a conventional reagent bath consisting of methylolated methylolmelamine and a cross-linking agent, such as dimethyloldihydroxyethyleneurea and a catalyst, such as zinc nitrate or magnesium chloride. This same patent illustrates also, the introduction of an aqueous emulsion of polyurthanes into fabric in a separate step to develop a fiber coating that enhances abrasion resistance. In general, the benefits are less than desired from such modifications of conventional cross-linking treatments.
In U.S. Pat. No. 3,606,992 there is described a method for treating cotton-containing fabric for obtaining improved wrinkle-resistance and improved abrasion resistance which involves padding the fabric through a resin finishing bath containing a mixture of a conventional thermo-setting resin in combination with a latex emulsion prior to a subsequent drying step, and a final curing at elevated temperature. In this case the additive is a synthetic rubber latex, which consists of a carboxy-modified butadiene-styrene copolymer in emulsion form. This preformed polymer undergoes some reaction with the resin forming reagents to produce a coating on fabric, yarn and fiber surfaces.
U.S. Pat. No. 3,311,496 describes a process that involves pretreatment of fabric with hardenable aminoplasts by the wet steam process before treatment with crease-proofing hardenable aminoplasts. At a given level of wrinkle recovery, the tensile strength of the product is significantly higher than that of the unpretreated fabric. U.S. Pat. No. 2,992,138 teaches to overcome adverse effects upon tensile strength of fabrics caused by zinc nitrate catalyst employed with dimethylolethyleneurea by introducing an alkali metal acetate into the reagent mixture. U.S. Pat. No. 3,402,988 achieves improved abrasion resistance and other properties by first impregnating fabric with conventional wash-wear formulations, and second applying a catalyst deactivator on the top and bottom of the fabric, so that superior properties are retained in the surface area. According to U.S. Pat. No. 3,634,019 high strength losses in cellulosic fabrics when treated with crease proofing agents to produce durable-press properties are avoided by eliminating a major part of the usual acidic catalyst and adding an amount of zinc or aluminum acetate.
In U.S. Pat. No. 3,807,952 there is described, a method for improving abrasion resistance in crosslinked cellulosic fibers which amounts to introducing salt additives to the conventional reagent system. U.S. Pat. No. 3,827,994 refers to imparting abrasion resistance and permanent press properties to cellulosic materials by employing N-methylollactamide in conjunction with other N-methylol reagents. U.S. Pat. No 3,526,474 describes a process for imparting abrasion resistance and wrinkle resistance and durable-press properties to cellulosic fibers by first applying the N-methylol reagent and subjecting it to curing conditions in the presence of a so-called polymerization catalyst and later impregnating the treated fabric with latent acid catalyst, drying and finally curing. U.S. Pat. No. 3,656,885 achieves improvement in wear resistance of cotton fabrics in wash-wear or durable-press garments by sequentially seperate steps of swelling, substitution, and crosslinking of fabric and, more specifically applying to cotton pairs of monofunctional and polyfunctional reactive swelling agents.
In the above-cited prior art and conventional processes for development of easy-care or durable-press properties in cotton fabrics, the N-methylol resins reduce the hydrophilic characteristics of the original cotton fiber, and this is further accentuated and aggravated by introduction of supplementary additives into the reagent system. The result is that the hydrophilic characteristics of the cotton are further reduced. Since the cotton fiber is unique among major textile fibers for apparel in its hydrophilic characteristics, it is undesirable that these be lost; in general, reduction of hydrophilic characteristics of cotton results in decreased moisture regain, decreased water imbibition, and decreased comfort to a wearer.